1. Field of the Invention
The present invention relates to electronic circuit boards and, particularly, to an electronic circuit board having a plurality of electrode terminals connected to an electronic component or another electronic circuit board by using flowable conducting material.
2. Description of Related Art
Various recent electrical products have a semiconductor device such as a transistor and IC or an electric component such as a capacitor and filter that is surface-mounted on a packaging substrate.
Particularly in the field of small-size portable electronic equipment such as mobile phones and portable digital cameras, there has been remarkable progress in the development of lighter, thinner, shorter and smaller products. Accordingly, development of lighter, thinner, shorter and smaller electronic components to be mounted on electronic equipment is proceeding rapidly.
In smaller and highly functional electronic components, the pitch of electrode terminals formed therein is narrow. Accordingly, the pitch of electrode terminals formed on a packaging substrate where an electronic component is mounted is also narrow. Further, the distance between electronic components is short due to high density packaging of electronic components on a packaging substrate.
As a reference technique, Japanese Unexamined Patent Publication No. 2004-47781 discloses a board where four slit grooves are formed in a pad on the board. The four slit grooves extend from the center of the pad to open toward the middle of four sides of the pad. When a circuit element is mounted on the pad of the board, flux contained in solder is collected in the four slit grooves, thereby preventing generation of a flux collective portion between the circuit element and the pad.
As another reference technique, Japanese Unexamined Patent Publication No. 2003-347356 discloses a technique that includes a plurality of pads formed on the rear surface of a semiconductor chip, grooves formed in the periphery of the plurality of pads, and grooves extending from a part of the periphery of the pad to the peripheral end of the semiconductor chip in such a way that they open outward at the peripheral end. When the semiconductor chip is mounted to a packaging substrate, excess of molten solder runs into the grooves formed on the rear surface of the semiconductor chip, thereby producing a thinner semiconductor device.
Narrow pitch of electrode terminals formed on a board on which an electronic component is to be mounted and small interval between electrode components in small, highly functional, and high density packaging electronic components cause short-circuit between adjacent electrode terminals to occur when surface-mounting the electronic component onto the board due to flowable conducting material such as solder.
Short-circuit between electrode terminals is likely to occur particularly when surface-mounting a high frequency device having high frequency characteristics onto a packaging substrate. This is described hereinafter in detail.
The high frequency device is produced by mounting a plurality of high frequency electronic components on the surface of a board for high frequency device and packaging those high frequency electronic components with resin, for example. Further, a plurality of electrode terminals are formed on the rear surface of the board for high frequency device, and those electrode terminals are connected to electrode terminals on the packaging substrate by flowable conducting material such as solder.
The high frequency device is composed of high frequency electronic components such as a semiconductor chip, transistor, IC, diode, chip capacitor, chip resistor, surface acoustic wave (SAW) filter, and inductor, a module that combines these components, and so on. The semiconductor chip, transistor, IC and diode form a semiconductor device. The chip capacitor, chip resistor, SAW filter and inductor form a passive circuit device.
The high frequency wave refers to communication wave, microwave, submillimeter wave, millimeter wave and so on that are used in various mobile communication, satellite broadcasting and wireless LAN (WLAN).
In order for the high frequency device to have high frequency characteristics, it is necessary to place a ground electrode terminal on substantially the whole area of the rear surface of the high frequency device board from its center part to peripheral part. A plurality of high frequency electronic components and so on are mounted on the surface of the high frequency device board.
This structure minimizes the connection between the ground electrode terminal of the high frequency electronic component that is formed on the front surface of the high frequency device board and the ground electrode terminal of the high frequency device board that is formed on the rear surface of the high frequency device board to minimize reactance component, thereby maintaining high frequency characteristics of high frequency electronic components.
Further, the ground electrode terminal on the rear surface of the high frequency device board is formed in a wide range so as to include the area immediately below a strip line path that is formed on the front surface of the high frequency device board. This prevents a change in characteristics impedance of the strip line path, thereby maintaining high frequency characteristics of high frequency electronic components.
It is particularly effective to form the ground electrode terminal on the rear surface of the high frequency device board in a wide range so as to include the area immediately below a strip line path that is formed on the front surface of the high frequency device board if a high frequency device includes a distributed constant circuit.
In addition, since the high frequency electronic components are placed at the end part of the high frequency device, if the strip line path needs to be drawn to the end of the high frequency device board, it is necessary to form the ground electrode terminal on the rear surface of the high frequency device board in a still wider range from the center to the peripheral part of the high frequency device board.
As described above, in order for the high frequency device to have high frequency characteristics, it is necessary to place the ground electrode terminal on substantially the whole area of the rear surface of the high frequency device board from its center part to near end part.
The distance between a ground electrode terminal and an electrode terminal adjacent to the ground electrode terminal is thereby narrowed. This causes solder bridge to occur when surface-mounting the high frequency device onto an electronic circuit board. Short-circuit between electrode terminals is thus likely to occur.
The narrow pitch of electrode terminals formed on a board on which electronic components are to be mounted in small, highly functional, and high density packaging electronic components causes short-circuit between adjacent electrode terminals due to flowable conducting material such as solder. Further, the small distance between electrode components also causes short-circuit between adjacent electrode terminals to occur when surface-mounting electronic components onto the board due to flowable conducting material such as solder.